The present invention relates to burnable substrates such as mosquito coils for dispensing air treatment chemicals. More particularly it relates to ways of achieving desired air treatment effects using lower levels of air treatment chemicals.
Insect control ingredients, fragrances, and other air treatment chemicals have been dispensed into the air by a variety of types of dispensers. Some use an electrical heater to volatize the active into the air from a wick, mat, or other substrate. Others use a fan to blow active off of a porous substrate into the air.
Another approach is to use a burning device to dispense the active. For example, candles having wicks have had fragrance, citronella, and other air treatment chemicals mixed with their wax such that as the wax is consumed by the candle the active is dispensed.
Such candles have been formed in a variety of configurations. See eg. U.S. Pat. No. 6,371,755. However, this approach requires a burning flame (which is susceptible to being blown out, which restricts where the candle can be placed, and restricts the actives).
Still another approach is to use a burnable object which consumes itself without a flame. Insect control coils (e.g. “mosquito coils”) and incense punks are of this type. They can be manufactured at very low cost (e.g. making them particularly suitable for use in impoverished countries that have severe malaria control issues).
Mosquito coils typically have a generally spiral-shaped body with is composed of a slowly burnable solid material that is impregnated or coated with an insect control active ingredient (such as a repellant, an insecticide, or an insect growth regulator). When the coil burns, the heat from the burning vaporizes and disperses the insect control active ingredient. Examples of such coils are disclosed in U.S. Pat. Nos. 4,144,318, 5,657,574, 5,948,424, 6,419,898, 6,732,473, and 6,941,697.
It is desirable that such a coil burn very slowly as such coils are often intended to provide protection for eight hours or so (e.g. overnight). Further, coil materials must be designed to be consumed so that they don't easily snuff out before the coil is used up and so that they don't readily burst into flames after the initial lighting. Another constraint is that they cannot be so brittle as to present undesirable breakage risks. This can be a significant consideration given the inherent nature of dough derived cellulosic materials and that such coils are often supported only at discrete positions (e.g. their centers) to reduce the risk of snuffing.
Further they must also be made of materials that don't interfere with the active in undesirable ways (e.g. react with the active during storage; retard dispensing of active too much). Also, any ingredient of the coil should not significantly increase the overall cost of the coil over standard ingredients, given that typical users of such coils are often extremely poor.
Such coils have therefore traditionally been made of largely cellulosic secondary/by product powder materials (e.g. coconut or peanut shell flour, sawdust, ground leaves, ground bark), sometimes with small amounts of additives that will affect burning characteristics or appearance, modify production characteristics, or act as a preservative (e.g. binder starch, kerosene, potassium chloride, or dye). While existing coils made from these materials have proven quite useful, there is a desire to improve them further.
For example, in order to achieve desired extended burn times using such conventional ingredients one must typically make the coil of a certain minimum size (which, if it could be reduced without cutting back on burning time could lead to cost savings and consumer preference). Also, many such coils are manufactured using wet extrusion followed by a drying step to create the desired rigidity. Some active can be prematurely volatized during the drying step, thereby increasing the cost of the active (as more needs to be added to achieve a given result during burning).
Further, many coils uniformly mix active throughout the coil. As a result, some of the active can be destroyed or partially degraded during the burning process before it is able to be dispensed. Also, because active will to some extent slowly volatize from standard coils in storage (absent precautions) they must be packaged in relatively expensive sealed packaging prior to use. This increases the cost of the ultimate product to the consumer.
Hence, a need exists for insect control coils which achieve improvements with respect to the above concerns.